Here in Ky, I was run out of a stream that I'd been fishing by a Cottonmouth...very aggressive...held him off with the tip of my rod till I got to shore...I was wading, fishing for Smallmouth bass.
While I've rarely carried for that specific reason, I do pack a S&W 36 with snake loads while fishing in NC. The rocky gorges that I fish do have Copperheads, and I've killed two in the last ten years or so.
I'm a live and let live guy...the snakes are usually after mice etc. but one that's harboring where kids and other fishermen are tromping around is a menace and needs to be dealt with. The 'snake loads' that I put up use #12 shot over a full dose of Unique or Bullseye and will do the trick out to about ten feet max. I use one 'snake load' per cylinder full, and 125 gr +P's for the rest. Ten feet is plenty of standoff distance, and beats trying to find a good stick to do the job while keeping a wary eye on that bad guy.
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USAF Forward Air Controller, 5th Spl Forces,
An Loc, lll Corps, RVN, 69-70, Vietnam Vet '69-'73